Prior art off-road bicycles include one in which the front wheel is supported by a front wheel suspension having a buffering mechanism and an attenuating mechanism, as disclosed in Japanese Patent Laid-Open Publication H2-231289. This front wheel suspension comprises a steering bracket rotatably supported in a front portion of the bicycle frame and a pair of, i.e., left and right, front fork assemblies coupled together by the steering bracket. Each of the front fork assemblies includes an inner tube and an outer tube, which are slidable relative to each other. In these tubes, an oil chamber and a gas chamber are formed. Gas in the gas chamber functions as a buffering mechanism, and the oil chamber is provided with an attenuating mechanism.
Regarding this prior art front wheel suspension, when the front fork assemblies are elongated and contracted by impact forces exerted from the front wheel, the gas in the gas chambers in the front fork assemblies functions to absorb the impact forces, while attenuating forces that are generated as the oil in the oil chambers flows through the attenuating mechanisms suppresses the elongating or contracting motion of the front fork assemblies to suppress vibrations.
In the prior art bicycle suspension of this type, in order to provide for desired level of riding comfort, depending on the taste and weight of the rider, an air valve is provided at the upper end of each front fork assembly for changing the gas pressure (i.e., air pressure) in the gas chambers, thus adjusting the pneumatic spring reaction force.
In the above prior art front wheel suspension, in order to pressurize the inside of the gas chambers, a gas supply (i.e., an air supply) has to be connected to the gas valves. In addition, for reducing pressure in the gas chambers, an exhausting means has to be mounted on the gas valves. Since the gas chamber pressure adjustment requires the accessory equipment such as the gas supply and exhausting means, it is impossible to adjust the pneumatic spring reaction force while the bicycle is in use.